A phased array antenna uses multiple radiating elements to transmit, receive, or transmit and receive radio frequency (RF) signals. Phased array antennas may be used in various capacities, including communications on the move (COTM) antennas, communications on the pause (COTP) antennas, satellite communication (SATCOM) airborne terminals, SATCOM mobile communications, Local Multipoint Distribution Service (LMDS), wireless point to point (PTP) microwave systems, and SATCOM earth terminals. Furthermore, the typical components in a phased array antenna are distributed components that are therefore frequency sensitive and designed for specific frequency bands. A typical SATCOM systems has a forward link that is time division multiplexed (TDM) and a return link that is time division multiple access (TDMA). Receive and transmit functions need not be accomplished simultaneously and synchronization and time standards for synchronizations are typical factors in most, if not all, of the aforementioned communication systems for operational bandwidth efficiency.
A typical electronically steerable phased array antenna comprises an assembly of phase shifters, power splitters, power combiners, and hybrids. Additionally, a typical electronically steerable phased array requires at least a few of these components at every radiating element in the phased array, which increases the cost and complexity of the architecture. Additionally, an electronically steerable phased array antenna is more complex if operating as a half-duplex function. A half-duplex phased array antenna is configured to transmit and receive through the same radiating element.
A typical digital phase shifter uses switched delay lines, is physically large, and operates over a narrow band of frequencies due to its distributed nature. Another type of typical digital phase shifter implements a switched high-pass low-pass filter architecture which has better operating bandwidth compared to a switched delay line but is still physically large. Also, these phase shifters are often made on gallium arsenide (GaAs). Though other materials may be, used, GaAs is a higher quality material designed and controlled to provide good performance of electronic devices. However, in addition to being a higher quality material than other possible materials, GaAs is also more expensive and more difficult to manufacture. The typical phased array components take up a lot of area on the GaAs, resulting in higher costs. Furthermore, a standard phase shifter involving solid state circuits has high radio frequency (RF) power loss, which is typically about (2*n) dB of loss, where n is the number of phase bits in the phase shifter. Another prior art embodiment uses RF MEMS switches and has lower power loss but still consumes similar space and is generally incompatible with monolithic solutions.
In addition to digital phase shifters, quadrature hybrids or other differential phase generating hybrids are also used in a variety of RF applications. In an exemplary embodiment, quadrature hybrids are used for generating circular polarization signals, power combining, or power splitting. In an exemplary embodiment, the outputs of a quadrature hybrid have equal amplitude and a nominally 90° phase difference. In another typical embodiment, the quadrature hybrid is implemented as a distributed structure, such as a Lange coupler, a branchline coupler, and/or the like. A 180° hybrid, such as a magic tee or a ring hybrid, results in a nominally 180° phase shift. In general, quadrature hybrids and 180° hybrids are limited in frequency bandwidth and require significant physical space. Additionally, since the structures are distributed in nature, their physical size increases with decreasing frequency. Moreover, the quadrature hybrids and 180° hybrids are typically made of GaAs and have associated RF power loss on the order of 3-4 dB per hybrid when used as a power splitter, and an associated RF power loss of about 1 dB when used as a power combiner.
In-phase power combiners and in-phase power splitters are also used in a variety of RF applications. In an exemplary embodiment, the outputs of an in-phase hybrid have equal amplitude and a substantially zero differential phase difference. In another exemplary embodiment, the inputs of an in-phase hybrid configured as a power combiner encounter substantially zero differential phase and amplitude shift. In a prior art embodiment, the in-phase hybrid is implemented as a distributed structure such as a Wilkinson coupler. In general, an in-phase hybrid is limited in frequency band and requires significant physical space. Additionally, since the structure is distributed in nature, the physical size increases with decreasing frequency. The in-phase hybrid is typically made of GaAs. Moreover, the in-phase hybrid generally has associated RF power loss on the order of 3-4 dB per hybrid when used as a power splitter and an associated RF power loss of about 1 dB when used as a power combiner.
Additionally, typical phased array antennas only form a single beam at a time and are often not capable of polarization agility. In order to form additional beams and/or have polarization agility ability from the same radiating aperture, additional phase shifting and power splitting or combining components are required at every radiating element. These additional components are typically distributed in nature, require significant physical space, are lossy, and only operate over relatively narrow frequency bands. For these reasons, polarization agile, multiple beam phased array antennas that can operate over multiple frequency bands are difficult to realize in practice. Furthermore, the typical components in a phased array antenna are distributed components that are therefore frequency sensitive and designed for specific frequency bands.
The polarizer of a prior art phased array antenna is typically specific to a particular polarization. It may be linear, circular, or elliptical, but in general is not able to be electronically reconfigured to handle different polarizations. Furthermore, a typical communications-based phased array antenna only uses a radiating element for either transmitting or receiving, but does not switch between the two functions. This is generally due to the transmit and receive frequency bands being sufficiently far apart to preclude a single radiating element from supporting both bands with adequate efficiency.
Thus, a need exists for a phased array antenna that is not frequency limited or polarization specific. Also, a need exists for an antenna polarizer that is reconfigurable for different polarizations, and able to transmit and receive using the same radiating element in half-duplex fashion.